arXiv subjects

Zoran Ristivojevic

Publications and source records attributed to Zoran Ristivojevic.

49 records · Page 3Linked to original sources

arXiv2012

Exact asymptotic behavior of correlation functions for disordered spin-1/2 XXZ chains

We consider an XXZ spin-1/2 chain in the presence of several types of disorder that do not break the XY symmetry of the system. We calculate the complete asymptotic form of the spin-correlation functions at zero temperature at the transition between liquid and disordered phase that occurs for a special value of anisotropy in the limit of small disorder. Apart from a universal power law decay of correlations, we find additional logarithmic corrections due to marginally irrelevant operator of disorder.

cond-mat.stat-mech↗

arXiv2012

Phase transition of interacting disordered bosons in one dimension

Interacting bosons generically form a superfluid state. In the presence of disorder it can get converted into a compressible Bose glass state. Here we study such transition in one dimension at moderate interaction using bosonization and renormalization group techniques. We derive the two-loop scaling equations and discuss the phase diagram. We find that the correlation functions at the transition are characterized by universal exponents in a finite region around the fixed point.

cond-mat.dis-nn↗

arXiv2012

A Monte Carlo simulation of ion transport at finite temperatures

We have developed a Monte Carlo simulation for ion transport in hot background gases, which is an alternative way of solving the corresponding Boltzmann equation that determines the distribution function of ions. We consider the limit of low ion densities when the distribution function of the background gas remains unchanged due to collision with ions. A special attention has been paid to properly treat the thermal motion of the host gas particles and their influence on ions, which is very important at low electric fields, when the mean ion energy is comparable to the thermal energy of the host gas. We found the conditional probability distribution of gas velocities that correspond to an ion of specific velocity which collides with a gas particle. Also, we have derived exact analytical formulas for piecewise calculation of the collision frequency integrals. We address the cases when the background gas is monocomponent and when it is a mixture of different gases. The developed techniques described here are required for Monte Carlo simulations of ion transport and for hybrid models of non-equilibrium plasmas. The range of energies where it is necessary to apply the technique has been defined. The results we obtained are in excellent agreement with the existing ones obtained by complementary methods. Having verified our algorithm, we were able to produce calculations for Ar$^+$ ions in Ar and propose them as a new benchmark for thermal effects. The developed method is widely applicable for solving the Boltzmann equation that appears in many different contexts in physics.

physics.plasm-ph↗

arXiv2011

Interaction effects on thermal transport in quantum wires

We develop a theory of thermal transport of weakly interacting electrons in quantum wires. Unlike higher-dimensional systems, a one-dimensional electron gas requires three-particle collisions for energy relaxation. The fastest relaxation is provided by the intrabranch scattering of comoving electrons which establishes a partially equilibrated form of the distribution function. The thermal conductance is governed by the slower interbranch processes which enable energy exchange between counterpropagating particles. We derive an analytic expression for the thermal conductance of interacting electrons valid for arbitrary relation between the wire length and electron thermalization length. We find that in sufficiently long wires the interaction-induced correction to the thermal conductance saturates to an interaction-independent value.

cond-mat.mes-hall↗

arXiv2010

Interaction-induced corrections to conductance and thermopower in quantum wires

We study transport properties of weakly interacting spinless electrons in one-dimensional single channel quantum wires. The effects of interaction manifest as three-particle collisions due to the severe constraints imposed by the conservation laws on the two-body processes. We focus on short wires where the effects of equilibration on the distribution function can be neglected and collision integral can be treated in perturbation theory. We find that interaction-induced corrections to conductance and thermopower rely on the scattering processes that change number of right- and left-moving electrons. The latter requires transition at the bottom of the band which is exponentially suppressed at low temperatures. Our theory is based on the scattering approach that is beyond the Luttinger-liquid limit. We emphasize the crucial role of the exchange terms in the three-particle scattering amplitude that was not discussed in the previous studies.

cond-mat.mes-hall↗

arXiv2010

A proposal to detect vortices above the superconducting transition temperature

We propose a simple experiment to determine whether vortices persist above the superconducting transition temperature Tc in the pseudogap phase of high temperature cuprate superconductors. This involves using a magnetic dot to stabilize a vortex in a thin cuprate film beneath the dot. We calculate the magnetic field profile as a function of distance from the dot if a vortex is present, and discuss possible measurements that could be done to detect this. Finally, we comment on the temperature range where a stable vortex should be observable.

cond-mat.supr-con↗

arXiv2010

Superconducting film with randomly magnetized dots: A realization of the 2D XY model with random phase shifts

We consider a thin superconducting film with randomly magnetized dots on top of it. The dots produce a disordered pinning potential for vortices in the film. We show that for dots with permanent and random magnetization normal or parallel to the film surface, our system is an experimental realization of the two-dimensional XY model with random phase shifts. The low-temperature superconducting phase, that exists without magnetic dots, survives in the presence of magnetic dots for sufficiently small disorder.

cond-mat.supr-con↗

arXiv2010

Spin-filtering by field dependent resonant tunneling

We consider theoretically transport in a spinfull one-channel interacting quantum wire placed in an external magnetic field. For the case of two point-like impurities embedded in the wire, under a small voltage bias the spin-polarized current occurs at special points in the parameter space, tunable by a single parameter. At sufficiently low temperatures complete spin-polarization may be achieved, provided repulsive interaction between electrons is not too strong.

cond-mat.str-el↗

arXiv2009

Transport in a Luttinger liquid with dissipation: two impurities

We consider theoretically the transport in a one-channel spinless Luttinger liquid with two strong impurities in the presence of dissipation. As a difference with respect to the dissipation free case, where the two impurities fully transmit electrons at resonance points, the dissipation prevents complete transmission in the present situation. A rich crossover diagram for the conductance as a function of applied voltage, temperature, dissipation strength, Luttinger liquid parameter K and the deviation from the resonance condition is obtained. For weak dissipation and 1/2<K<1, the conduction shows a non-monotonic increase as a function of temperature or voltage. For strong dissipation the conduction increases monotonically but is exponentially small.

cond-mat.str-el↗

arXiv2009

Ground state configurations of vortices in superconducting film with magnetic dot

We consider a thin superconducting film with a magnetic dot with permanent magnetization (normal to the film) placed on it by a method based on London-Maxwell equations. For sufficiently high dot magnetization a single vortex appears in the ground state. Further increase of magnetization is accompanied with the appearance of antivortices and more vortices in the film. We study analytically conditions for the appearance of a vortex--antivortex pair for a range of parameters. The phase diagram with diversity of vortex--antivortex states is calculated numerically. When appear in the ground state, antivortices are at distances comparable to the dot radius. For not too large dot radii the total vorticity in the ground state is predominantly zero or one. Magnetic field due to the dot and vortices everywhere in space is calculated analytically.

cond-mat.supr-con↗

arXiv2008

Multigrid solver for axisymmetrical 2D fluid equations

We have developed an efficient algorithm for steady axisymmetrical 2D fluid equations. The algorithm employs multigrid method as well as standard implicit discretization schemes for systems of partial differential equations. Linearity of the multigrid method with respect to the number of grid points allowed us to use $256\times 256$ grid, where we could achieve solutions in several minutes. Time limitations due to nonlinearity of the system are partially avoided by using multi level grids(the initial solution on $256\times 256$ grid was extrapolated steady solution from $128\times 128$ grid which allowed using "long" integration time steps). The fluid solver may be used as the basis for hybrid codes for DC discharges.

physics.plasm-ph↗

arXiv2008

Transport in a Dissipative Luttinger Liquid

We study theoretically the transport through a single impurity in a one-channel Luttinger liquid coupled to a dissipative (ohmic) bath . For non-zero dissipation $η$ the weak link is always a relevant perturbation which suppresses transport strongly. At zero temperature the current voltage relation of the link is $I\sim \exp(-E_0/eV)$ where $E_0\simη/κ$ and $κ$ denotes the compressibility. At non-zero temperature $T$ the linear conductance is proportional to $\exp(-\sqrt{{\cal C}E_0/k_BT})$. The decay of Friedel oscillation saturates for distance larger than $L_η\sim 1/η$ from the impurity.

cond-mat.mes-hall↗

arXiv2007

The Effect of Randomness on the Mott State

We reinvestigate the competition between the Mott and the Anderson insulator state in a one-dimensional disordered fermionic system by a combination of instanton and renormalization group methods. Tracing back both the compressibility and the ac-conductivity to a vanishing kink energy of the electronic displacement field we do not find any indication for the existence of an intermediate (Mott glass) phase.

cond-mat.str-el↗